//将两个升序链表合并为一个新的 升序 链表并返回。新链表是通过拼接给定的两个链表的所有节点组成的。 
//
// 
//
// 示例 1： 
//
// 
//输入：l1 = [1,2,4], l2 = [1,3,4]
//输出：[1,1,2,3,4,4]
// 
//
// 示例 2： 
//
// 
//输入：l1 = [], l2 = []
//输出：[]
// 
//
// 示例 3： 
//
// 
//输入：l1 = [], l2 = [0]
//输出：[0]
// 
//
// 
//
// 提示： 
//
// 
// 两个链表的节点数目范围是 [0, 50] 
// -100 <= Node.val <= 100 
// l1 和 l2 均按 非递减顺序 排列 
// 
// Related Topics 递归 链表 
// 👍 2654 👎 0

package leetcode.editor.cn;
/**
 * [21]合并两个有序链表
 */
public class MergeTwoSortedLists {
    public static void main(String[] args) {
        Solution solution = new MergeTwoSortedLists().new Solution();
        ListNode first = new MergeTwoSortedLists.ListNode(1);
        first.next = new MergeTwoSortedLists.ListNode(2);
        first.next = new MergeTwoSortedLists.ListNode(4);

        ListNode second = new MergeTwoSortedLists.ListNode(1);
        second.next = new MergeTwoSortedLists.ListNode(3);
        second.next = new MergeTwoSortedLists.ListNode(4);

        ListNode result = solution.mergeTwoLists(first, second);
        System.out.println(result);
    }
    //leetcode submit region begin(Prohibit modification and deletion)
/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
static class ListNode {
    int val;
    ListNode next;
    ListNode() {}
    ListNode(int val) { this.val = val; }
    ListNode(int val, ListNode next) { this.val = val; this.next = next; }
}
class Solution {
    public ListNode mergeTwoLists(ListNode list1, ListNode list2) {
        ListNode head = new ListNode();
        ListNode index = head;
        ListNode first = list1;
        ListNode second = list2;
        while (first != null && second != null) {
            if (first.val < second.val) {
                index.next = first;
                first = first.next;
            } else {
                index.next = second;
                second = second.next;
            }
            index = index.next;
        }
        index.next = first != null? first:second;
        return head.next;
    }
}
//leetcode submit region end(Prohibit modification and deletion)

}